What is the regulator doing?
The exhaust gases emitted by ship diesel engines, contain a variety of substances. For international regulation the most important substances are sulphur oxides (SOx, caused by the sulphur contents in fuel), nitrous oxides (NOx), carbon dioxide (CO2) and particulate matter (PM). Marpol Annex VI is the IMO regulation which limits the emissions of these substances. See http://www.imo.org/OurWork/Environment/PollutionPrevention/AirPollution/Pages/The-Protocol-of-1997-%28MARPOL-Annex-VI%29.aspx
A good overview of the current regulatory framework and pipeline has been put together by ABS and can be downloaded here: ABS Regulatory landscape
For SOx the worldwide cap currently is 3.5%, decreasing to 0.5% in 2020. In SOX Emission Control Areas (SECA, ao North Sea, Baltic, N-American coastal waters) the SOx emissions are limited to 0.1% from 1 January 2015. SOx emissions can be cut down in 2 ways: either by burning low-sulphur fuel or by using exhaust gas after treatment (sulphur scrubber).
Particulate Matter (PM)
Particulate Matter (PM) is regarded as a by-effect of SOx emissions, hence with SOx reductions, PM will go down as well.
For NOx emissions the regulation is depending on the type of engine and the year it was constructed. According to IMO proposals, the NOx emission of certain ships will have to be reduced considerably in 2016. Furthermore, there will be reductions is NOx Emission Control Areas (NECA). See http://www.theicct.org/sites/default/files/publications/ICCT_MarineSCR_Mar2014.pdf
CO2 emissions are directly related to the use of fossil fuels. Heavy Fuel Oil (HFO) and Marine Diesel (MDO) are the primary fuels for ships, and although ships are relatively energy-efficient means of transport, the overall GHG emissions from the maritime sector are substantial, being 2-3% of global emissions (the size of Germany’s emissions). Currently there is no general regulation in place for the reduction of emissions, with the inustry relying on the EEDI (for new builds) and SEEMP (for efficient operations) which are currently inadequate to meet the increasing challenge of decarbonisation in the industry. The debate at IMO has moved on from ways to define energy efficiency and Monitoring, Reporting and Verification of energy performance data with the introduction of the EU-MRV which came into force in 2015, with data collection from 2018 and the subsequent IMO DCS system, which is similar coming nito force in 2018 and collecting data from the beginning of 2019.